| Abstract
| - This paper describes an integrated experimental andcomputational framework for developing 3-D structuralmodels for humic acids (HAs). This approach combinesexperimental characterization, computerassisted structureelucidation (CASE), and atomistic simulations to generateall 3-D structural models or a representative sample ofthese models consistent with the analytical data and bulkthermodynamic/structural properties of HAs. To illustratethis methodology, structural data derived from elementalanalysis, diffuse reflectance FT-IR spectroscopy, 1-D/2-D1H and 13C solution NMR spectroscopy, and electrosprayionization quadrupole time-of-flight mass spectrometry (ESIQqTOF MS) are employed as input to the CASE programSIGNATURE to generate all 3-D structural models for Chelseasoil humic acid (HA). These models are subsequentlyused as starting 3-D structures to carry out constanttemperature-constant pressure molecular dynamicssimulations to estimate their bulk densities and Hildebrandsolubility parameters. Surprisingly, only a few modelisomers are found to exhibit molecular compositions andbulk thermodynamic properties consistent with theexperimental data. The simulated 13C NMR spectrum ofan equimolar mixture of these model isomers comparesfavorably with the measured spectrum of Chelsea soil HA.
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